in piñon-juniper woodlands

Funding: DOE-EPSCoR, DOE-BER

Objective: The Southwestern U.S. has already experienced changes in climate that have altered precipitation patterns, and models currently predict an imminent transition to a warmer, more arid climate in this region in the coming decades. One of the questions we have been working on is quantifying the impact these droughts and related disturbances have on both local and regional carbon storage, hydrologic partitioning and water resources. We are also trying to quantify how resilient biomes across the NMEG have been to these disturbances and predict how this may change with predicted climate change scenarios. In my lab, we have focused particularly on the widespread piñon tree mortality throughout New Mexico, Arizona, Utah and Colorado in piñon-juniper woodlands (PJ) following the turn of the century drought (1999-2002). Abrupt mortality of 40-95% of piñon pine (Pinus edulis) and 2-25% of juniper (Juniperus monosperma) occurred in less than 3 years throughout the region. Climate projections suggest that episodic droughts, such as the one correlated with these recent conifer mortality events are likely to increase in frequency and severity and expand northward. Given the spatial extent of PJ woodlands (3rd largest biome in the US) and climatic predictions of increased frequency and intensity of drought in the region, it is crucial to understand the consequences of these disturbances on regional carbon and energy dynamics, biogeochemical processes and atmospheric CO2.

We initiated a manipulative study to quantify the consequences of widespread tree mortality on ecosystem carbon and water cycling. We experimentally simulated piñon mortality by killing all of the adult piñon trees in an intact PJ woodland within a 200 m fetch of an eddy covariance tower in September 2009. We have been comparing fluxes in this site to those measured in an intant, undisturbed piñon-juniper woodland that is <5 km away continuously since then. We received follow-up funding from DOE BER in 2012 to continue and expand this research to produce: 1) a quantitative description of the short term (3-4 y) and extended (5-10 y) impact of piñon mortality on the regional carbon and water fluxes to the atmosphere (Morillas et al. JGR-Biogeosciences; Fox et al. paper in prep); 2) an evaluation of various satellite based remote sensing platforms to detect the sensitivity of detecting stress and recovery in disturbed PJ woodlands (Eitel et al. 2011; Krofcheck et al 2014, 2015); 3) an understanding of the mechanisms controlling the response and recovery of ecosystem production and respiration processes following piñon mortality (Berryman et al. 2013, Warnock et al. 2016 a,b, Dean et al. 2015; Liebricht et al., in prep), and improvements in the ability of a land surface model, CLM, to represent these mortlaity events to predict the trajectory of disturbed woodlands, and estimate both the current and future impact of piñon mortality on carbon and water storage across the region. Results for this experiment has also been included in some recent syntheses (Anderegg et al. 2015; McDowell et al. 2013).